Conventional ornamental stitch sewing machines utilize separate cams for respectively controlling lateral movement of the needle bar and the forward and reverse movements of the feed dog. A set of cams, whether of the drop-in type or of the built-in type, for controlling the movements of the needle bar, generally includes a more frequently used cam for producing an ordinary zig-zag stitch, as well as other less frequently used cams, for producing a variety of different stitch patterns. In the case of drop-in type cams, such cams conventionally are formed of molded plastic material in a double tier formation, with one cam controlling the movement of the needle bar and the other cam controlling the movement of the feed dog. Thus, each conventional drop-in cam actually comprises a pair of cams integral with each other so that both cams must be used in the machine simultaneously to obtain a particular stitch pattern. In such an arrangement a relatively large number of double cams are required to be made available in order to cover a particular range of stitch patterns. For example, if a cam (A) which controls the feed dog is combined with each one of different cams (B,C,D, and E), each of which controls the lateral movement of the needle bar, four such double cams are required to produce a particular range of stitch patterns. Thus, in the above example, cam A, which performs a particular function, is repeated four times, once in each of the four combinations.
In the case where a plurality of built-in cams is incorporated in a machine, a relatively complex cam selection mechanism is required to be used to effect shifting of the cam followers into registration with desired cams.
In accordance with my invention, I provide on a drive shaft a built-in feed cam for controlling the forward and reverse movements of the feed dog, such cam cooperating with a registering follower or tracking element, the movement of which may be modified by other conventional mechanism. Also, coaxially mounted on the shaft is a conventional zig-zag cam for controlling the lateral movement of the needle bar. The zig-zag cam is axially slidable on the shaft and normally is spring biased to register with a second cam tracking element operatively connected to the needle bar. The shaft is adapted to removably receive a third cam, one of a series of ornamental stitch cams. Said third cam when mounted on the shaft displaces the zig-zag cam but is itself disposed and maintained in registration with the second cam tracking element. In such condition, the zig-zag cam is rendered ineffective. However, upon removal of the third cam, the zig-zag cam automatically returns to its normal operative position in registration with the second tracking element. Thus, with my invention only a single cam is required to be replaced to vary the ornamental stitch pattern. The zig-zag cam which most frequently is used by an operator is merely temporarily displaced from operative position by the ornamental stitch cam and need not be removed from the shaft to accommodate the ornamental cam.